Conventionally, in carrier wireless communication, a base station device that is a wireless communication device is provided with an amplifier that amplifies a transmission signal. The transmission signal amplified by the amplifier generally includes nonlinear distortion. Therefore, the base station device sends, via an antenna, a transmission signal subjected to distortion compensation to compensate for the nonlinear distortion. FIG. 13A is a block diagram illustrating an example of a base station device according to a conventional technology. FIG. 13A illustrates only blocks related to distortion compensation of the transmission signal and sending from the antenna, and other blocks are omitted.
For example, as illustrated in FIG. 13A, a base station device 10 according to the conventional technology includes a digital pre distortion controller (DPDC) 110 and an amplifier 160. The DPDC 110 performs distortion compensation on a transmission signal input to the amplifier 160 so that distortion of the transmission signal to be output from the amplifier 160 can be reduced. The transmission signal output from the DPDC 110 is converted to a radio frequency (RF) signal by a block including a digital-to-analog (DA) converter 120, a mixer 130, a phase locked loop (PLL) 140, and an amplifier 150, and input to the amplifier 160.
Then, the transmission signal amplified by the amplifier 160 is sent from an antenna 100 via a block including a coupler 170, an isolator 180, a duplexer 190, and a coupler 200. Furthermore, the transmission signal amplified by the amplifier 160 is split by the coupler 170, and input, as a feedback signal, to a switch 210. The feedback signal input to the switch 210 is converted to a baseband signal by a block including a mixer 220, a PLL 230, and an analog-to-digital (AD) converter 240, and input to the DPDC 110. The feedback signal is input to the DPDC 110 through a route 1 illustrated in FIG. 13A. The DPDC 110 performs distortion compensation on the transmission signal based on the feedback signal so that a distortion value of the transmission signal amplified by the amplifier 160 can be reduced.
In addition, the DPDC 110 detects a reflected wave coming from the antenna 100 through a route 3 illustrated in FIG. 13A, monitors a voltage standing wave ratio (VSWR), and detects an abnormality of the antenna 100. The DPDC 110 detects an abnormality of the antenna 100 on the basis of the VSWR based on the reflected wave input via a block including the coupler 200, the switch 210, the mixer 220, the PLL 230, and the AD converter 240. Incidentally, the base station device 10 switches between input from the coupler 170 to the DPDC 110 and input from the coupler 200 to the DPDC 110 by using the switch 210; however, input from each of the couplers may independently be input to the DPDC 110.
Patent Literature 1: Japanese Laid-open Patent Publication No. 2006-197545
Patent Literature 2: Japanese National Publication of International Patent Application No. 2009-545250
Patent Literature 3: Japanese Laid-open Patent Publication No. 2014-090299
In some cases, due to a change in a load state of the antenna 100, the transmission signal output from the amplifier 160 may be reflected from the antenna 100. If the transmission signal is reflected from the antenna 100, a reflected wave may be input to the switch 210 through a route 2 illustrated in FIG. 13A. In this case, the DPDC 110 performs distortion compensation based on a signal, in which a feedback signal of the transmission signal and the reflected wave are superimposed. Specifically, even if the characteristics of the transmission signal at an output end of the amplifier 160 is set to an optimum value, a divergence between the transmission signal and the feedback signal occurs depending on the load state of the antenna 100 connected to the base station device 10, and distortion included in the transmission signal may be increased.
For example, as illustrated in FIG. 13A, the DPDC 110 performs distortion compensation based on the feedback signal, in which the reflected wave obtained through the route 2 is superimposed on the transmission signal obtained through the route 1, so that a divergence between the transmission signal and the feedback signal occurs. Consequently, in the above-described technology, as illustrated in FIG. 13B, distortion included in the transmission signal subjected to the distortion compensation is increased, and the quality of the transmission signal is reduced.